Scubapro MK20 - shredded piston O-ring

[herman]

If you guys are interested in orings, I suggest you read Parker's Oring manual (on line). They have some excellent information on how oring seals work. They suggest considering an oring to be like an elastic, very thick liquid that "flows" into the space around it when forced to do so by pressure but it can't flow past a give gap, creating a seal. Wheather or not the oring will flow through the gap (extrude) is determined by the " viscosity" of the oring (durometer), the differential pressure across it and the width of the gap. They also discuss back up rings and dynamic vs static, something which most people don't really understand. Very worthwhile reading for anyone who wants to understand how a dive regulator works since orings are a vital part of them......or nerds who just love to know how stuff works.

 

[fmerkel]

That's not a manual, it's a college education! The first explanatory section was pretty readable and understandable, at least for me. The point about extrusion under pressure was conveyed quite well.
Good link. Thanks.

E. In either static or dynamic O-ring seals under high pres-
sure the primary cause of seal failure is extrusion of the
seal material into the piston-cylinder clearance. The
major factors effecting extrusion are fluid pressure, seal
hardness and strength, and piston-cylinder clearance.

F. Dynamic seals may fail by abrasion against the cylinder
or piston walls. Therefore, the contacting surfaces should
be polished for long seal life. Moving seals that pass over
ports or surface irregularities while under hydraulic pres-
sure are very quickly cut or worn to failure.